Semiconductor packaging structure and method

ABSTRACT

A system and method for packaging semiconductor dies is provided. An embodiment comprises a first package with a first contact and a second contact. A post-contact material is formed on the first contact in order to adjust the height of a joint between the contact pad a conductive bump. In another embodiment a conductive pillar is utilized to control the height of the joint between the contact pad and external connections.

This application is a continuation of Ser. No. 15/230,921, entitled“Semiconductor Packaging Structure and Method,” filed on Aug. 8, 2016,which application is a divisional of U.S. patent application Ser. No.13/357,379, entitled “Semiconductor Packaging Structure and Method,”filed on Jan. 24, 2012, now U.S. Pat. No. 9,412,689, issued on Aug. 9,2016, which applications are incorporated herein by reference.

BACKGROUND

Generally, in a Package on Package (PoP) system individual semiconductordies may be packaged either separately (or with multiple semiconductordies in each separate package), and then the separate packages may bebrought together and interconnected so that the individual semiconductordies in the separate packages may be integrated together in order toperform a desired tasks. The individual packages may be electricallyinterconnected to each other, for example, by using contact bumps.

Such contact bumps may be formed by initially forming a layer of thecontact material onto a substrate of the package. Once the layer of thecontact material has been formed, the layer of contact material may bereflowed, by which the temperature of the contact material is increasedin order to at least partially liquefy the contact material. Thispartial liquification allows the contact material to pull itself into aball shape using its own surface tension.

Once formed, the contact bumps of one package may be placed into contactwith contact pads from another package. Alternatively, the contact bumpsmay be placed into contact with other types or forms of contacts formedon the other package. Once the contact bumps have been aligned withtheir appropriate locations, the contact bumps may again be reflowed andreheated in order to again partially liquefy them and cause them topartially flow and form a bridge between the two packages. Once thecontact bumps cool down and resolidify, the contact bumps are fullyjoined to each other. This joint between the contact bumps allows forboth a physical connection between the contact bumps as well as anelectrical connection that allows signals and power to cross from onepackage to another, thereby allowing the two packages to be integratedwith each other and work together.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a first package with first contacts and secondcontacts in accordance with an embodiment;

FIG. 2 illustrates the formation of post-contact material onto the firstcontact in accordance with an embodiment;

FIG. 3 illustrates the formation of contacts onto the post-contactmaterial in accordance with an embodiment;

FIG. 4 illustrates the bonding of a second package onto the firstpackage in accordance with an embodiment;

FIG. 5 illustrates a bonding of a third package onto the first packagein accordance with an embodiment;

FIG. 6 illustrates a forming of conductive pillars on the contact padsin accordance with an embodiment;

FIG. 7 illustrates a forming a barrier layer onto the conductive pillarsin accordance with an embodiment;

FIG. 8 illustrates a forming of bumps on the conductive pillars inaccordance with an embodiment; and

FIG. 9 illustrates a bonding of the second package and the third packageto the first package in accordance with an embodiment.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The embodiments will be described with respect to embodiments in aspecific context, namely a contact structure for a package-on-package(PoP) architecture. The embodiments may also be applied, however, toother packaging architectures and other contact structures.

With reference now to FIG. 1, there is shown a first package 100 with asubstrate 101, through substrate vias 103 extending from a first side102 of the substrate 101 to a second side 104 of the substrate 101. Afirst redistribution layer 105, first contact pads 109, second contactpads 108, a first passivation layer 110, and first UBMs 112 may belocated on the first side 102 of the substrate 101. A secondredistribution layer 111, third contacts 117, second UBMs 121, and asecond passivation layer 119 may be located on the second side 104 ofthe substrate 101.

The substrate 101 for the first package 100 may be, e.g., a siliconsubstrate, doped or undoped, or an active layer of asilicon-on-insulator (SOI) substrate, used to provide support for thefirst package 100. However, the substrate 101 may alternatively be aceramic substrate, a polymer substrate, an interposer, or any othersubstrate that may provide a suitable protection and/or fan-outstructure that may be desired. These and any other suitable materialsmay alternatively be used for the substrate 101.

The through substrate vias 103 may extend from the first side 102 of thesubstrate 101 to the second side 104 of the substrate 101, and may beformed by any appropriate method. For example, in an embodiment openingsare formed partially through the substrate 101. The openings may beformed, for example, by one or more etching processes, milling, lasertechniques, or the like. The openings are lined with diffusion barrierlayers, adhesion layers, isolation layer, or the like, and filled with aconductive material. Preferably, diffusion barrier layers (not shown),comprise one or more layers of TaN, Ta, TiN, Ti, CoW, or the like, andthe conductive material comprises copper, tungsten, aluminum, silver,and combinations thereof, or the like, thereby forming the throughsubstrate vias 103. In an embodiment, the through substrate vias 103have a diffusion barrier layer of TaN and are filled with copper formedby an electro-chemical plating process in which a seed layer isdeposited to aid in the formation of the conductive fill material.

In another embodiment, the through substrate vias 103 may be formed andfilled with a dielectric material. After grinding the backside of thesubstrate 101, the dielectric material may then be removed via anetching process. Once removed, the dielectric material may be replacedwith a conductive material, such as copper. Other methods and materialsmay be used.

The first redistribution layer 105 may be formed on the first side 102of the substrate 101 and in electrical connection with the throughsubstrate vias 103. The first redistribution layer 105 may extend awayfrom the through substrate vias 103 and allow for the placement of thefirst contact pads 109 (discussed further below) anywhere desired. Thefirst redistribution layer 105 may also be used to enlarge the pitch ofthe through substrate vias 103 in a fan-out pattern or else reduce thepitch of the through substrate vias 103.

The first redistribution layer 105 may be formed using common methodsfor forming interconnect lines in integrated circuits. Preferably, thefirst redistribution layer 105 comprises at least one conductive layerformed of a metal such as aluminum, copper, tungsten, titanium, andcombinations thereof. The at least one conductive layer may be formed byplating the metal on a seed layer and then etching the undesiredportions, leaving the at least one conductive layer, which may have athickness of between about 2 μm and about 30 μm, with a preferred widthof about 5 μm. Once the at least one conductive layer has been formed, adielectric material may be formed over the at least one conductivelayer, and vias may be formed through the dielectric material to provideelectrical access to the at least one conductive layer. However, othermaterials and process, such as a well-known damascene process, couldalternatively be used to form the first redistribution layer 105.

As one of skill in the art will recognize, the first redistributionlayer 105 could be a single layer of conductive material or else couldalternatively be multiple layers of conductive material, depending uponthe properties desired. For example, the first redistribution layer 105as formed above may be plated with another conductive material such asgold or chromium to provide good adhesion for a subsequently formedconnector (described below). This plating could be done through aprocess such as CVD.

The first contact pads 109 and the second contact pads 108 may be formedin order to provide external contacts for the first redistribution layer105. In an embodiment the second contact pads 108 may be used to provideexternal contacts from the first package 100 to a second package 400(not illustrated in FIG. 1 but illustrated and discussed below withrespect to FIG. 4). Additionally, the first contact pads 109 may be usedto provide external contacts to a third package 500 (also notillustrated in FIG. 1 but illustrated and discussed below with respectto FIG. 5).

The first contact pads 109 and the second contact pads 108 and may beformed of a conductive material such as aluminum, although othersuitable materials, such as copper, tungsten, or the like, mayalternatively be utilized. The first contact pads 109 and the secondcontact pads 108 may be formed using a process such as CVD, althoughother suitable materials and methods may alternatively be utilized. Oncethe material for the first contact pads 109 and the second contact pads108 has been deposited, the material may be shaped into the firstcontact pads 109 using, e.g., a photolithographic masking and etchingprocess.

After the first contact pads 109 and the second contact pads 108 havebeen formed, a first passivation layer 110 may be formed to help isolateand protect the first contact pads 109 and the second contact pads 108.In an embodiment the first passivation layer 110 may be formed from apolymer such as polyimide, or may alternatively be formed of materialssuch as silicon oxides, silicon nitrides, low-k dielectrics, extremelylow-k dielectrics, combinations of these, and the like. The firstpassivation layer 110 may be formed to have a thickness of between about2 μm and about 15 μm, such as about 5 μm.

Once the first passivation layer 110 has been formed, the first UBMs 112may be formed in contact with the first contact pads 109 and the secondcontact pads 108. In an embodiment the first UBMs 112 may be formed byinitially forming an opening for the first UBMs 112 through the firstpassivation layer 110 using, e.g., a photolithographic masking andetching process. Once at least a portion of the first contact pads 109and the second contact pads 108 have been exposed, the first UBMs 112may be formed in electrical contact with the first contact pads 109 andthe second contact pads 108. The first UBMs 112 may comprise threelayers of conductive materials, such as a layer of titanium, a layer ofcopper, and a layer of nickel. However, one of ordinary skill in the artwill recognize that there are many suitable arrangements of materialsand layers, such as an arrangement of chrome/chrome-copperalloy/copper/gold, an arrangement of titanium/titanium tungsten/copper,or an arrangement of copper/nickel/gold, that are suitable for theformation of the first UBMs 112. Any suitable materials or layers ofmaterial that may be used for the first UBMs 112 are fully intended tobe included within the scope of the embodiments.

The first UBMs 112 may be created by forming each layer over the firstcontact pads 109 and the second contact pads 108. The forming of eachlayer may be performed using a plating process, such as electrochemicalplating, although other processes of formation, such as sputtering,evaporation, or PECVD process, may alternatively be used depending uponthe desired materials. The first UBMs 112 may be formed to have athickness of between about 0.7 μm and about 10 μm, such as about 5 μm.Once the desired layers have been formed, portions of the layers maythen be removed through a suitable photolithographic masking and etchingprocess to remove the undesired material and to leave the first UBMs 112in a desired shape, such as a circular, octagonal, square, orrectangular shape, although any desired shape may alternatively beformed.

On the second side 104 of the substrate 101, the second redistributionlayer 111, the third contacts 117, the second passivation layer 119, andthe second UBMs 121 may be formed in order to provide for a connectivityfrom the through substrate vias 103 to external devices (not shown inFIG. 1). In an embodiment, the second redistribution layer 111, thethird contacts 117, the second passivation layer 119, and the secondUBMs 121 may be formed in similar fashions and from similar materials asthe first redistribution layer 105, the first contact pads 109, and thefirst passivation layer 110, and the first UBMs 112, respectively,described above. However, the second redistribution layer 111, the thirdcontacts 117, the second passivation layer 119, and the second UBMs 121may alternatively be formed using different methods and materials.

Once the second UBMs 121 have been formed on the second side 104 of thesubstrate 101, first conductive connectors 123 may be formed over thesecond UBMs 121. The first conductive connectors 123 may be, e.g.,contact bumps and may comprise a material such as tin, or other suitablematerials, such as silver, lead-free tin, or copper. In an embodiment inwhich the first conductive connectors 123 are tin solder bumps, thefirst conductive connectors 123 may be formed by initially forming alayer of tin through such commonly used methods such as evaporation,electroplating, printing, solder transfer, ball placement, etc, to athickness of, e.g., about 100 μm. Once a layer of tin has been formed onthe structure, a reflow may be performed in order to shape the materialinto the desired bump shape.

However, the described embodiments are not intended to be limited to acontact bump as described above. Any other suitable contact connection,such as a copper connection, a conductive pillar (such as a copperpillar), or any other type of connection may alternatively be utilized.All suitable connections are fully intended to be included within thescope of the embodiments.

FIG. 2 illustrates the formation of a post-contact material 201 on thefirst UBMs 112. In an embodiment the post-contact material 201 may beused to adjust the height of the joint between the first UBMs 112 andthe second conductive connectors 301 (not illustrated in FIG. 2 butillustrated and described below with respect to FIG. 3). In anembodiment in which the second conductive connectors 301 are solderballs, the post-contact material 201 may be, e.g., a high melting pointpre-solder such as SnCu, SnAg, SnAgCu, or SnAu, combinations of these,or the like. The post-contact material 201 may be printed onto the firstUBMs 112, although other processes, such as electroplating orelectroless plating, may alternatively be utilized.

In an embodiment, the post-contact material 201 may be formed to have afirst thickness T₁ that is large enough to reduce or eliminate thepossibility of a cold joint between the first UBMs 112 and the secondconductive connectors 301. In an embodiment, the first thickness T₁ maybe between about 10 μm and about 200 μm, such as about 100 μm. However,while these thicknesses are illustrative, the first thickness T₁ is notintended to be limited to these thicknesses, as any suitable thicknessmay alternatively be utilized as needed to prevent a cold joint fromoccurring.

FIG. 3 illustrates that, after the post-contact material 201 has beenformed, second conductive connectors 301 may be formed on thepost-contact material 201. In an embodiment the second conductiveconnectors 301 may be similar to the first conductive connectors 123,and may be, e.g., conductive bumps such as solder bumps, and maycomprise a material such as tin, or other suitable materials, such assilver, lead-free tin, or copper. Alternatively, the second conductiveconnectors 301 may be a material such as SnZn, SnBi, SnIn, SnCd,combinations of these, or the like, and which may have a melting pointthat is lower than the post-contact material 201. In an embodiment inwhich the second conductive connectors 301 are tin solder bumps, thesecond conductive connectors 301 may be formed by initially forming alayer of tin through such commonly used methods such as evaporation,electroplating, printing, solder transfer, ball placement, etc, to athickness of, e.g., about 100 μm. Once a layer of tin has been formed onthe structure, a reflow may be performed in order to shape the materialinto the desired bump shape.

FIG. 4 illustrates a bonding and encapsulation of a second package withthe first package 100. In an embodiment the second package 400 may be apackage for a semiconductor die (not individually illustrated in FIG. 4)upon which various active and passive devices (such as transistor,resistors, capacitors, inductors, and the like) have been formed inorder to create a functional device. The semiconductor die may alsocomprise an alternating series of conductive and dielectric layers overthe active and passive devices in order to interconnect and isolate thevarious devices and to form functional circuitry.

Additionally, in order to connect the functional circuitry to the firstpackage 100, the first die may be packaged within the second package400, and the second package 400 may have fourth contacts 403 to connectthe second package 400 with the second contact pads 108 on the firstpackage 100. The fourth contacts 403 may be a conductive material, suchas copper, and may be, e.g., in the shape of a conductive pillar. Thefourth contacts 403 may be formed utilizing, e.g., a photolithographicand plating process, forming the fourth contacts 403 in electricalcontact with the underlying conductive layers of the second package 400and the active and passive devices of the semiconductor die within thesecond package 400 in order to provide the external contact for theseactive and passive devices. However, the fourth contacts 403 are notintended to be limited to copper pillars, as any suitable type ofcontact, such as aluminum contact pads, solder bumps, wire bond pads, orthe like, may alternatively be utilized.

The fourth contacts 403 (located on the second package 400) may beconnected to the second contact pads 108 (located on the first package100) using, e.g., a bonding process. In an embodiment the bondingprocess may comprise forming or otherwise placing a first connectingmaterial 405, such as solder, on the fourth contacts 403, the secondcontact pads 108, or both. The fourth contacts 403 and the secondcontact pads 108 may then be placed in contact with each other (with thefirst connecting material 405 between them) and the first connectingmaterial 405 may be reflowed in order to bond the second contact pads108 to the fourth contacts 403 and also to bond the second package 400to the first package 100.

Once the second package 400 has been bonded to the first package 100,the structure may be encapsulated using an encapsulant 407, such asmolding compound, polyimide, PPS, PEEK, PES, a heat resistant crystalresin, combinations of these, or the like. In an embodiment the bondedfirst package 100 and second package 400 may be placed in a moldingchamber (not illustrated), and the encapsulant 407 may be injected orotherwise placed into the molding chamber. The molding chamber shapesthe encapsulant 407 into the desired shape in order to encapsulate thesecond package 400 on the first package 100 in order to provide supportand protection to the second package 400. Once in place, the encapsulant407 may be cured in order to harden the encapsulant 407 for optimumprotection. While the exact curing process is dependent at least in parton the particular material chosen for the encapsulant 407, in anembodiment in which molding compound is chosen as the encapsulant 407,the curing could occur through a process such as heating the encapsulant407 to between about 100° C. and about 130° C., such as about 125° C.for about 60 sec to about 3000 sec, such as about 600 sec. Additionally,initiators and/or catalysts may be included within the encapsulant 407to better control the curing process.

FIG. 5 illustrates the placement and bonding of a third package 500 ontothe first package 100. In an embodiment the third package 500 may,similar to the second package 400, be a package for a semiconductor dieupon which various active and passive devices (not individuallyillustrated in FIG. 5) may be formed. The third package 500 maysimilarly have fifth contacts 501 that may be electrically connected tothe active and passive devices within the semiconductor die within thethird package 500. The fifth contacts 501 may be formed from similarprocesses and materials as the fourth contacts 403 (described above withrespect to FIG. 4), although the fifth contacts 501 may alternatively bemade from different materials and different processes.

The third package 500 may be bonded to the first package 100 similar tothe bonding process described above with respect to FIG. 4. For example,the bonding process may comprise placing the fifth contacts 501 and thefirst contact pads 109 in contact with each other (with the secondconductive connectors 301 between them) and the second conductiveconnectors 301 may be reflowed in order to bond the first contact pads109 to the fifth contacts 501 and also to bond the third package 500 tothe first package 100.

FIG. 6 illustrates another embodiment in which conductive pillars 601are utilized to control the joint height instead of the post-contactmaterial 201. In this embodiment the conductive pillars 601 may beformed by initially forming a photoresist (not shown) over the firstpassivation layer 110 to a thickness greater than about 20 μm, or evengreater than about 60 μm. The photoresist may be patterned to exposeportions of the first passivation layer 110 through which the conductivepillars 601 will extend. Once patterned, the photoresist may then beused as a mask to remove the desired portions of the first passivationlayer 110, thereby exposing those portions of the first contact pads 109to which the conductive pillars 601 will make contact.

After the first passivation layer 110 has been patterned, the conductivepillars 601 may be formed within the openings of both the firstpassivation layer 110 as well as the photoresist. The conductive pillars601 may be formed from a conductive material such as copper, althoughother conductive materials such as nickel, gold, or metal alloy,combinations of these, or the like may also be used. Additionally, theconductive pillars 601 may be formed using a process such aselectroplating, by which an electric current is run through theconductive portions of the first contact pads 109 to which theconductive pillars 601 are desired to be formed, and the first contactpads 109 are immersed in a solution. The solution and the electriccurrent deposit, e.g., copper, within the openings in order to filland/or overfill the openings of the photoresist and the firstpassivation layer 110, thereby forming the conductive pillars 601.Excess conductive material outside of the openings may then be removedusing, for example, a chemical mechanical polish (CMP).

After the conductive pillars 601 have been formed, the photoresist maybe removed through a process such as ashing, whereby the temperature ofthe photoresist is increased until the photoresist decomposes and may beremoved. After the removal of the photoresist, the conductive pillars601 extend away from the first passivation layer 110 a first distance d₁of between about 10 mm to about 300 mm, such as about 180 mm.

However, as one of ordinary skill in the art will recognize, the abovedescribed process to form the conductive pillars 601 is merely one suchdescription, and is not meant to limit the embodiments to this exactprocess. Rather, the described process is intended to be merelyillustrative, as any suitable process for forming the conductive pillars601 may alternatively be utilized. For example, forming the firstpassivation layer 110 to a thickness greater than its eventualthickness, forming the conductive pillars 601 into an opening of thefirst passivation layer 110, and then removing a top portion of thefirst passivation layer 110 such that the conductive pillars 601 extendaway from the first passivation layer 110 may also be utilized. Allsuitable processes are fully intended to be included within the scope ofthe present embodiments.

FIG. 7 illustrates an optional barrier layer 701 that may be formed overthe conductive pillars 601. The barrier layer 701 may be tin or otherconductive material and may be formed by a process such as immersion Sn(IT), organic solderability preservative (OSP), self-assembled monolayer(SAM), electroless nickel electroless palladium immersion gold (ENEPIG),combinations of these, or the like. The barrier layer 701 may be formedto a thickness of between about 0.1 μm and about 10 μm, such as about0.5 μm.

FIG. 8 illustrates another embodiment in which the conductive pillars601 are optionally capped with a conductive material 801. In anembodiment the conductive material 801 may be, e.g., a non-flow soldercap, such as SnZn, SnBi, SnIn, SnCd, or the like. The non-flow soldercap may be formed by electroplating, electroless plating, immersionplating, or the like, to a thickness of between about 1 μm and about 100μm, such as about 20 μm.

Alternatively, the conductive material 801 may be a flowable materialsuch as a solder. In this embodiment the conductive material 801 may besimilar to the material of the first conductive connector 123, such as atin solder bump formed by plating and a reflow process. However, theconductive material 801 may alternatively be any other suitableconductive material.

FIG. 9 illustrates the placement and bonding of the second package 400and the third package 500 onto the first package 100. In an embodimentthe second package 400 and the third package 500 may be bonded to thefirst package 100 using methods and processes similar to those describedabove with respect to FIG. 4 and FIG. 5, such as by aligning andreflowing a conductive material under pressure to bond the secondpackage 400 and the third package 500. However, any other suitablemethod of bonding the second package 400 and the third package 500 tothe first package 100 may alternatively be utilized.

In accordance with an embodiment, a semiconductor device comprising afirst package with a first side and a first contact located on the firstside and a second contact located on the first side is provided. A firstpost-contact material is over the first contact but not over the secondcontact.

In accordance with another embodiment, a semiconductor device comprisinga first contact and a second contact on a first side of a first packageis provided. A conductive pillar extends away from the first contact,wherein the second contact is free from a conductive pillar.

In accordance with yet another embodiment, a method for forming asemiconductor device comprising forming a first contact and a secondcontact on a first package is provided. A height of the first contact isadjusted relative to the second contact by forming a post-contactmaterial over the first contact.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. For example,the precise methods and materials used to form the various structuresmay be altered while still remaining within the scope of theembodiments. Additionally, the precise placement of the contact pads onthe first package may be changed to suit the design needs of the firstpackage while remaining within the scope of the embodiments.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the embodiments, processes, machines,manufacture, compositions of matter, means, methods, or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein may be utilized according to theembodiments. Accordingly, the appended claims are intended to includewithin their scope such processes, machines, manufacture, compositionsof matter, means, methods, or steps.

What is claimed is:
 1. A method for forming a semiconductor device, themethod comprising: forming a first external conductive connector inphysical contact with a first post-contact material over a firstunderbump metallization of a first package, the first underbumpmetallization being over a first contact, wherein the first externalconductive connector comprises a single material throughout the firstexternal conductive connector, wherein the single material, the firstcontact, the first underbump metallization and the first post-contactmaterial each have a different composition from each other; and bondinga second package to a second underbump metallization over a secondcontact, wherein the first external conductive connector extends awayfrom the first package a first distance, the second package extends awayfrom the first package a second distance, the second distance beingparallel to and less than the first distance, and wherein the secondpackage comprises a second conductive connector in physical contact withthe second underbump metallization.
 2. The method of claim 1, furthercomprising forming through substrate vias in the first package prior tothe forming the first external conductive connector.
 3. The method ofclaim 2, wherein the forming the through substrate vias comprises:forming an opening in a substrate of the first package; filling theopening with a conductive material; and thinning the substrate to exposethe conductive material.
 4. The method of claim 2, wherein the formingthe through substrate vias comprises: forming an opening in a substrateof the first package; filling the opening with a dielectric material;thinning the substrate to expose the dielectric material; and replacingthe dielectric material with a conductive material.
 5. The method ofclaim 1, wherein the first contact is in electrical connection with thefirst package through a first redistribution layer.
 6. The method ofclaim 5, further comprising forming a second redistribution layer on anopposite side of the first package from the first redistribution layer.7. A method for forming a semiconductor device, the method comprising:applying a photoresist over a first contact and a second contact of afirst package; patterning the photoresist to expose a first region overthe first contact but not to expose a second region over the secondcontact; forming a copper pillar within the photoresist and inelectrical connection with the first contact; and bonding a secondpackage to the first package through the second contact, wherein thecopper pillar extends further from the first package than the secondpackage.
 8. The method of claim 7, further comprising forming a barrierlayer over the copper pillar.
 9. The method of claim 8, wherein theforming the barrier layer is performed at least in part with animmersion Sn process.
 10. The method of claim 8, wherein the forming thebarrier layer is performed at least in part with an organicsolderability preservative process.
 11. The method of claim 8, whereinthe forming the barrier layer is performed at least in part with aself-assembled monolayer process.
 12. The method of claim 7, furthercomprising forming a cap on the copper pillar.
 13. The method of claim12, wherein the forming the cap comprises forming a non-flow solder cap.14. The method of claim 12, wherein the forming the cap forms the cap toa thickness of between 1 μm and 100 μm.
 15. A method for forming asemiconductor device, the method comprising: applying a post contactmaterial to a first set of a first plurality of package contacts withoutapplying the post contact material to a second set of the firstplurality of package contacts, each of the first plurality of packagecontacts being located on a first side of a first package; bonding asecond package to the second set of the first plurality of packagecontacts, the second package comprising a first surface facing away fromthe first package; and forming a conductive element in physical contactwith the post contact material, the conductive element having a secondsurface facing away from the first package, the first surface beingcloser to the first package than the second surface.
 16. The method ofclaim 15, further comprising encapsulating the second package and theconductive element after the forming the conductive element.
 17. Themethod of claim 15, wherein the applying the post contact material isperformed at least in part through a printing process.
 18. The method ofclaim 15, further comprising forming external connectors on a secondside of the first package opposite the first side.
 19. The method ofclaim 18, wherein the external connectors are formed of a first materialand the post contact material comprises the first material.
 20. Themethod of claim 15, further comprising forming through vias that extendall of the way through the first package prior to the applying the postcontact material.